[flink] 01/02: [FLINK-24749] Add CachingSupplier

[ch...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

chesnay pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/flink.git

commit d4a0251a08ae1d5f931ab24dc898faea16e2a9a2
Author: Chesnay Schepler <ch...@apache.org>
AuthorDate: Wed Nov 3 13:59:26 2021 +0100

    [FLINK-24749] Add CachingSupplier
---
 .../flink/util/function/CachingSupplier.java       | 42 ++++++++++++++++++++++
 .../flink/util/function/CachingSupplierTest.java   | 39 ++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/flink-core/src/main/java/org/apache/flink/util/function/CachingSupplier.java b/flink-core/src/main/java/org/apache/flink/util/function/CachingSupplier.java
new file mode 100644
index 0000000..d1bfce1
--- /dev/null
+++ b/flink-core/src/main/java/org/apache/flink/util/function/CachingSupplier.java
@@ -0,0 +1,42 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.util.function;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.NotThreadSafe;
+
+import java.util.function.Supplier;
+
+/** A {@link Supplier} that returns a single, lazily instantiated, value. */
+@NotThreadSafe
+public class CachingSupplier<T> implements Supplier<T> {
+    private final Supplier<T> backingSupplier;
+    private @Nullable T cachedValue;
+
+    public CachingSupplier(Supplier<T> backingSupplier) {
+        this.backingSupplier = backingSupplier;
+    }
+
+    @Override
+    public T get() {
+        if (cachedValue == null) {
+            cachedValue = backingSupplier.get();
+        }
+        return cachedValue;
+    }
+}
diff --git a/flink-core/src/test/java/org/apache/flink/util/function/CachingSupplierTest.java b/flink-core/src/test/java/org/apache/flink/util/function/CachingSupplierTest.java
new file mode 100644
index 0000000..8826887
--- /dev/null
+++ b/flink-core/src/test/java/org/apache/flink/util/function/CachingSupplierTest.java
@@ -0,0 +1,39 @@
+package org.apache.flink.util.function;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import org.junit.jupiter.api.Test;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+
+class CachingSupplierTest {
+
+    @Test
+    void testCaching() {
+        final AtomicInteger instantiationCounts = new AtomicInteger();
+        final Supplier<Integer> backingSupplier = () -> instantiationCounts.incrementAndGet();
+        final CachingSupplier<Integer> cachingSupplier = new CachingSupplier<>(backingSupplier);
+
+        assertThat(cachingSupplier.get(), is(cachingSupplier.get()));
+        assertThat(instantiationCounts.get(), is(1));
+    }
+}